The present invention relates to motor vehicle seats of the known type comprising:
a squab including a frame which is intended to be mounted on the floor of the motor vehicle with the interposition of guide means for adjusting the position of the seat longitudinally of the motor vehicle, and
a backrest including a frame which is articulated at the bottom, about a first transverse axis, to a support structure fixed to the movable part of the longitudinal guide means, by means of a device which enables the angular position of the backrest to be adjusted relative to the transverse axis.
Recently, the constructional techniques relating to seats of the type indicated above have been directed increasingly to problems relating to the comfort of the user. On the one hand, there is the general problem of ensuring that the back, pelvis and legs of the seated person are supported as correctly as possible and, on the other hand, there is the problem caused by the considerable differences which may exist between possible users of the seat, in dependence on their height, weight and sex.
Notwithstanding the various studies which have already been carried out and the various propositions put forward, to the Applicant's knowledge, no motor vehicle seat has yet been produced which resolves the above problems in a completely satisfactory manner.
For example, various types of seat have been used which are provided with means for the adjustment of the curvature of the backrest in the region corresponding to the lumbar lordosis of the seated person. Whilst, on the one hand, they enable the lumbar region of the seated person's back to be supported correctly, these known solutions, on the other hand, generate new problems. For example, an increase in the curvature of the backrest to adapt it to a more pronounced lumbar lordosis at the same time creates a gap between the upper part of the backrest and the upper part of the back in the region adjacent the lordosis of the neck, which thus lacks support. Moreover, a different curvature of the backrest in the lumbar region generally forces the user to change the position of his back relative to the length of the motor vehicle, or causes a change in the distribution of the pressure exerted by the backrest on the back. It is essential, however, that the pressure distribution remains substantially constant under all conditions of use, in order to avoid the alteration of the optimum physiological conditions after a prolonged period in the seat. Finally, as already indicated, another problem results from the considerable differences which may exist between the physical characteristics of different users, particularly with reference to the vertical distance between the lordosis of the neck and the lumbar lordosis.
Another disadvantage of seats produced up to now lies in the fact that the lower axis of articulation of the backrest is situated adjacent the general plane of the backrest and therefore in a position a long way behind the imaginary axis of articulation between the legs and the body of the seated person. As a result of this situation, a variation in the inclination of the backrest also causes a variation in the vertical position of the seated person's back relative to the surface of the backrest. Thus, if the conformation of the surface of the backrest is adapted to the anatomy of the seated person's back with the backrest in a particular position, this condition is generally lost when the inclination of the backrest is changed.
Another problem common to all prior-art seats consists of the fact that the iliac region of the seated person is situated in correspondence with the angle formed between the squab and the backrest and therefore lacks support since the bulk of the adjacent parts of the padding of the backrest and the squab leaves an empty space in correspondence with the angle, which is not occupied by the body of the seated person.